diff --git a/LibTest/async/Completer/completeError_A01_t03.dart b/LibTest/async/Completer/completeError_A01_t03.dart
index f094aba929..31add756d9 100644
--- a/LibTest/async/Completer/completeError_A01_t03.dart
+++ b/LibTest/async/Completer/completeError_A01_t03.dart
@@ -19,7 +19,7 @@ main() {
 
   var v = [1,2,3];
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   var f = new Future.value(v).then((x) {
     asyncEnd();
@@ -34,4 +34,3 @@ main() {
 
   completer.completeError(f);
 }
-
diff --git a/LibTest/async/Completer/completeError_A01_t04.dart b/LibTest/async/Completer/completeError_A01_t04.dart
index c4deaeb9ed..5e4bd305ce 100644
--- a/LibTest/async/Completer/completeError_A01_t04.dart
+++ b/LibTest/async/Completer/completeError_A01_t04.dart
@@ -19,7 +19,7 @@ main() {
 
   var e = new Error();
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   var f = new Future.error(e).catchError((x) {
     asyncEnd();
diff --git a/LibTest/async/Future/Future.microtask_A01_t03.dart b/LibTest/async/Future/Future.microtask_A01_t03.dart
index f05085423e..9b1ea30a5e 100644
--- a/LibTest/async/Future/Future.microtask_A01_t03.dart
+++ b/LibTest/async/Future/Future.microtask_A01_t03.dart
@@ -22,7 +22,7 @@ main() {
   var completer2 = new Completer();
   Future future2 = new Future.microtask(() => completer2.future);
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   future
     .then((x) {
diff --git a/LibTest/async/Future/Future.sync_A01_t04.dart b/LibTest/async/Future/Future.sync_A01_t04.dart
index a19c62da21..71dd52a382 100644
--- a/LibTest/async/Future/Future.sync_A01_t04.dart
+++ b/LibTest/async/Future/Future.sync_A01_t04.dart
@@ -27,7 +27,7 @@ main() {
   var completer2 = new Completer();
   Future future2 = new Future.sync(() => completer2.future);
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   future
     .then((x) {
diff --git a/LibTest/async/Future/Future_A01_t03.dart b/LibTest/async/Future/Future_A01_t03.dart
index 3c7f0aafa9..f618e1173b 100644
--- a/LibTest/async/Future/Future_A01_t03.dart
+++ b/LibTest/async/Future/Future_A01_t03.dart
@@ -22,7 +22,7 @@ import "../../../Utils/expect.dart";
 
 main() {
   var value = [1, 2, 3];
-  asyncMultiStart(2);
+  asyncStart(2);
   Future future = new Future(() => new Future.value(value));
   Future future2 = new Future(() => new Future.error(value));
 
diff --git a/LibTest/async/Future/catchError_A01_t02.dart b/LibTest/async/Future/catchError_A01_t02.dart
index 6871c06302..9093dbd468 100644
--- a/LibTest/async/Future/catchError_A01_t02.dart
+++ b/LibTest/async/Future/catchError_A01_t02.dart
@@ -28,6 +28,6 @@ main() {
   f.catchError(onError1);
   f.catchError(onError2);
 
-  asyncMultiStart(2);
+  asyncStart(2);
   completer.completeError('!!!');
 }
diff --git a/LibTest/async/Future/catchError_A06_t01.dart b/LibTest/async/Future/catchError_A06_t01.dart
index 50cdc5a91b..818f5a6b32 100644
--- a/LibTest/async/Future/catchError_A06_t01.dart
+++ b/LibTest/async/Future/catchError_A06_t01.dart
@@ -25,7 +25,7 @@ check(value) {
   Completer completer = new Completer();
   Future f = completer.future;
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   f.catchError(
     (exception) {
diff --git a/LibTest/async/Stream/asBroadcastStream_A01_t05.dart b/LibTest/async/Stream/asBroadcastStream_A01_t05.dart
index 3051845b61..09220b1e0f 100644
--- a/LibTest/async/Stream/asBroadcastStream_A01_t05.dart
+++ b/LibTest/async/Stream/asBroadcastStream_A01_t05.dart
@@ -25,7 +25,7 @@ main() {
   );
   Stream b = controller.stream.asBroadcastStream();
   Expect.isFalse(hasListener);
-  asyncMultiStart(2);
+  asyncStart(2);
   b.listen(
     (_) {
       Expect.isTrue(hasListener);
diff --git a/LibTest/async/Stream/handleError_A04_t01.dart b/LibTest/async/Stream/handleError_A04_t01.dart
index f737538848..d5540eaff7 100644
--- a/LibTest/async/Stream/handleError_A04_t01.dart
+++ b/LibTest/async/Stream/handleError_A04_t01.dart
@@ -38,7 +38,7 @@ main() {
     asyncEnd();
   });
 
-  asyncMultiStart(N);
+  asyncStart(N);
 
   s3.listen((_) {
     Expect.fail('unexpected onData event');
diff --git a/LibTest/async/Stream/listen_A05_t01.dart b/LibTest/async/Stream/listen_A05_t01.dart
index a08418e243..933a707abd 100644
--- a/LibTest/async/Stream/listen_A05_t01.dart
+++ b/LibTest/async/Stream/listen_A05_t01.dart
@@ -33,7 +33,7 @@ main() {
     }
   });
 
-  asyncMultiStart(N);
+  asyncStart(N);
 
   s2.listen((_) {
     Expect.fail('unexpected call to onData');
diff --git a/LibTest/async/Stream/pipe_A04_t02.test.dart b/LibTest/async/Stream/pipe_A04_t02.test.dart
index d8421408ec..dc37140e1e 100644
--- a/LibTest/async/Stream/pipe_A04_t02.test.dart
+++ b/LibTest/async/Stream/pipe_A04_t02.test.dart
@@ -52,7 +52,7 @@ void test(CreateStreamFunction create) {
     }
   );
 
-  asyncMultiStart(2);
+  asyncStart(2);
   s.pipe(c).then(
       (_) {
         Expect.fail("Returned future should complete with error");
diff --git a/LibTest/async/StreamController/StreamController.broadcast_A01_t03.dart b/LibTest/async/StreamController/StreamController.broadcast_A01_t03.dart
index f1f1569383..3e351714e2 100644
--- a/LibTest/async/StreamController/StreamController.broadcast_A01_t03.dart
+++ b/LibTest/async/StreamController/StreamController.broadcast_A01_t03.dart
@@ -25,7 +25,7 @@ check(List events) {
   List expectedData = events.where((e) => !(e is num) || e >= 0).toList();
   List expectedErrors = events.where((e) => e is num && e < 0).toList();
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   List events1 = [], errors1 = [];
   s.listen(
diff --git a/LibTest/async/StreamController/StreamController.broadcast_A04_t02.dart b/LibTest/async/StreamController/StreamController.broadcast_A04_t02.dart
index 0125fe89d3..9526bde78a 100644
--- a/LibTest/async/StreamController/StreamController.broadcast_A04_t02.dart
+++ b/LibTest/async/StreamController/StreamController.broadcast_A04_t02.dart
@@ -18,7 +18,7 @@ import "../../../Utils/expect.dart";
 main() {
   StreamController controller = new StreamController.broadcast();
   Stream stream = controller.stream;
-  asyncMultiStart(2);
+  asyncStart(2);
   List log1 = [];
   StreamSubscription sub1 =
       stream.listen((event) => log1.add(event), onDone: () {
@@ -27,8 +27,7 @@ main() {
   });
 
   List log2 = [];
-  StreamSubscription sub2 =
-      stream.listen((event) => log2.add(event), onDone: () {
+  stream.listen((event) => log2.add(event), onDone: () {
     Expect.listEquals([1, 2, 3, 4, 5], log2);
     asyncEnd();
   });
diff --git a/LibTest/async/StreamController/StreamController.broadcast_A07_t03.dart b/LibTest/async/StreamController/StreamController.broadcast_A07_t03.dart
index dafd54b41e..6afc388b2f 100644
--- a/LibTest/async/StreamController/StreamController.broadcast_A07_t03.dart
+++ b/LibTest/async/StreamController/StreamController.broadcast_A07_t03.dart
@@ -16,7 +16,7 @@ import "../../../Utils/expect.dart";
 
 main() {
   int onCancelCallCount = 0;
-  asyncMultiStart(6);
+  asyncStart(6);
   StreamController? controller;
   controller = new StreamController.broadcast(
     onCancel: () {
diff --git a/LibTest/async/StreamController/StreamController.broadcast_A08_t01.dart b/LibTest/async/StreamController/StreamController.broadcast_A08_t01.dart
index f351a20399..86dd8b27dc 100644
--- a/LibTest/async/StreamController/StreamController.broadcast_A08_t01.dart
+++ b/LibTest/async/StreamController/StreamController.broadcast_A08_t01.dart
@@ -17,7 +17,7 @@ import "../../../Utils/expect.dart";
 main() {
   bool onListenCalled = false;
   bool onCancelCalled = false;
-  asyncMultiStart(4);
+  asyncStart(4);
 
   StreamController controller = new StreamController.broadcast(
     onListen: () {
@@ -44,4 +44,3 @@ main() {
 
   controller.close();
 }
-
diff --git a/LibTest/async/StreamTransformer/StreamTransformer_A03_t01.dart b/LibTest/async/StreamTransformer/StreamTransformer_A03_t01.dart
index fb6aa06209..36d57ffa1e 100644
--- a/LibTest/async/StreamTransformer/StreamTransformer_A03_t01.dart
+++ b/LibTest/async/StreamTransformer/StreamTransformer_A03_t01.dart
@@ -38,7 +38,7 @@ main() {
     }
   );
 
-  asyncMultiStart(3);
+  asyncStart(3);
 
   c.stream.transform(tr).listen(
     (x) {
diff --git a/LibTest/async/Zone/handleUncaughtError_A01_t04.dart b/LibTest/async/Zone/handleUncaughtError_A01_t04.dart
index 98016113ec..a37a55f67d 100644
--- a/LibTest/async/Zone/handleUncaughtError_A01_t04.dart
+++ b/LibTest/async/Zone/handleUncaughtError_A01_t04.dart
@@ -32,7 +32,7 @@ void test() {
   } catch (e, st) {
     stackTraces[count] = st;
 
-    asyncMultiStart(2);
+    asyncStart(2);
 
     new Future.error(e,st);
 
diff --git a/LibTest/html/Element/addEventListener_A01_t03.dart b/LibTest/html/Element/addEventListener_A01_t03.dart
index 7daa868623..f7e4577e2a 100644
--- a/LibTest/html/Element/addEventListener_A01_t03.dart
+++ b/LibTest/html/Element/addEventListener_A01_t03.dart
@@ -15,7 +15,7 @@ main() {
   var x = new ButtonElement();
   document.body?.append(x);
 
-  asyncMultiStart(3);
+  asyncStart(3);
 
   x.addEventListener(type, (e) {
     Expect.equals(type, e.type);
diff --git a/LibTest/html/Element/addEventListener_A01_t04.dart b/LibTest/html/Element/addEventListener_A01_t04.dart
index 69f722dc85..f9d8b6154d 100644
--- a/LibTest/html/Element/addEventListener_A01_t04.dart
+++ b/LibTest/html/Element/addEventListener_A01_t04.dart
@@ -16,7 +16,7 @@ main() {
   var x = new ButtonElement();
   document.body?.append(x);
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   // intercept on capture
   document.body?.addEventListener(type, (e) {
diff --git a/LibTest/html/Element/addEventListener_A01_t05.dart b/LibTest/html/Element/addEventListener_A01_t05.dart
index 07afc977c4..8363b1c347 100644
--- a/LibTest/html/Element/addEventListener_A01_t05.dart
+++ b/LibTest/html/Element/addEventListener_A01_t05.dart
@@ -17,7 +17,7 @@ main() {
 
   var n = 10;
 
-  asyncMultiStart(n);
+  asyncStart(n);
 
   EventListener genHandler() => (e) {
         Expect.equals(type, e.type);
diff --git a/LibTest/html/Element/addEventListener_A01_t06.dart b/LibTest/html/Element/addEventListener_A01_t06.dart
index 228b7d1d12..95c70c547a 100644
--- a/LibTest/html/Element/addEventListener_A01_t06.dart
+++ b/LibTest/html/Element/addEventListener_A01_t06.dart
@@ -17,7 +17,7 @@ main() {
 
   var n = 10;
 
-  asyncMultiStart(n);
+  asyncStart(n);
 
   EventListener genHandler() => (e) {
         Expect.equals(type, e.type);
diff --git a/LibTest/html/Element/removeEventListener_A01_t01.dart b/LibTest/html/Element/removeEventListener_A01_t01.dart
index 286a937019..b3a2692f85 100644
--- a/LibTest/html/Element/removeEventListener_A01_t01.dart
+++ b/LibTest/html/Element/removeEventListener_A01_t01.dart
@@ -33,7 +33,7 @@ main() {
   x.addEventListener(type, handler1);
   x.addEventListener(type, handler2);
 
-  asyncMultiStart(3); // first time two handlers, second time one handler
+  asyncStart(3); // first time two handlers, second time one handler
   var event = new Event(type);
   x.dispatchEvent(event);
   event = new Event(type);
diff --git a/LibTest/html/Element/removeEventListener_A01_t02.dart b/LibTest/html/Element/removeEventListener_A01_t02.dart
index 8cf3a0f354..22ed05a621 100644
--- a/LibTest/html/Element/removeEventListener_A01_t02.dart
+++ b/LibTest/html/Element/removeEventListener_A01_t02.dart
@@ -35,7 +35,7 @@ main() {
   body?.addEventListener(type, handler1, true);
   body?.addEventListener(type, handler2, true);
 
-  asyncMultiStart(3); // first time two handlers, second time one handler
+  asyncStart(3); // first time two handlers, second time one handler
   var event = new Event(type);
   x.dispatchEvent(event);
   event = new Event(type);
diff --git a/LibTest/html/Event/currentTarget_A01_t01.dart b/LibTest/html/Event/currentTarget_A01_t01.dart
index ac6ec07317..d9316cb3ac 100644
--- a/LibTest/html/Event/currentTarget_A01_t01.dart
+++ b/LibTest/html/Event/currentTarget_A01_t01.dart
@@ -24,6 +24,6 @@ main() {
     asyncEnd();
   });
 
-  asyncMultiStart(2);
+  asyncStart(2);
   div.dispatchEvent(new MouseEvent('click'));
 }
diff --git a/LibTest/html/Event/defaultPrevented_A01_t01.dart b/LibTest/html/Event/defaultPrevented_A01_t01.dart
index 1b657ff373..9a65b69aae 100644
--- a/LibTest/html/Event/defaultPrevented_A01_t01.dart
+++ b/LibTest/html/Event/defaultPrevented_A01_t01.dart
@@ -25,6 +25,6 @@ main() {
     asyncEnd();
   });
 
-  asyncMultiStart(2);
+  asyncStart(2);
   div.dispatchEvent(new MouseEvent('click'));
 }
diff --git a/LibTest/html/Event/eventPhase_A01_t01.dart b/LibTest/html/Event/eventPhase_A01_t01.dart
index 88fbc55d6a..22c1d43ddc 100644
--- a/LibTest/html/Event/eventPhase_A01_t01.dart
+++ b/LibTest/html/Event/eventPhase_A01_t01.dart
@@ -30,7 +30,7 @@ main() {
       asyncEnd();
     });
 
-    asyncMultiStart(3);
+    asyncStart(3);
     div.dispatchEvent(new MouseEvent('click'));
   } else {
     Expect.fail("Body is null");
diff --git a/LibTest/html/Event/matchingTarget_A01_t01.dart b/LibTest/html/Event/matchingTarget_A01_t01.dart
index ab454cbc50..7763be1d7c 100644
--- a/LibTest/html/Event/matchingTarget_A01_t01.dart
+++ b/LibTest/html/Event/matchingTarget_A01_t01.dart
@@ -38,7 +38,7 @@ main() {
       asyncEnd();
     });
 
-    asyncMultiStart(2);
+    asyncStart(2);
     id1.click();
     class1.click();
   } else {
diff --git a/LibTest/html/Event/target_A01_t01.dart b/LibTest/html/Event/target_A01_t01.dart
index 5ab9712980..876cfbe4bd 100644
--- a/LibTest/html/Event/target_A01_t01.dart
+++ b/LibTest/html/Event/target_A01_t01.dart
@@ -30,7 +30,7 @@ main() {
       asyncEnd();
     });
 
-    asyncMultiStart(3);
+    asyncStart(3);
     div.dispatchEvent(new MouseEvent('click'));
   } else {
     Expect.fail("Body is null");
diff --git a/LibTest/html/IFrameElement/addEventListener_A01_t03.dart b/LibTest/html/IFrameElement/addEventListener_A01_t03.dart
index 09da10fb47..9c2fde949f 100644
--- a/LibTest/html/IFrameElement/addEventListener_A01_t03.dart
+++ b/LibTest/html/IFrameElement/addEventListener_A01_t03.dart
@@ -15,7 +15,7 @@ main() {
   IFrameElement x = new IFrameElement();
   document.body?.append(x);
 
-  asyncMultiStart(3);
+  asyncStart(3);
 
   x.addEventListener(type, (e) {
     Expect.equals(type, e.type);
diff --git a/LibTest/html/IFrameElement/addEventListener_A01_t04.dart b/LibTest/html/IFrameElement/addEventListener_A01_t04.dart
index 09cf525d3b..2d2f7e6764 100644
--- a/LibTest/html/IFrameElement/addEventListener_A01_t04.dart
+++ b/LibTest/html/IFrameElement/addEventListener_A01_t04.dart
@@ -16,7 +16,7 @@ main() {
   IFrameElement x = new IFrameElement();
   document.body?.append(x);
 
-  asyncMultiStart(2);
+  asyncStart(2);
 
   // intercept on capture
   document.body?.addEventListener(type, (e) {
diff --git a/LibTest/html/IFrameElement/addEventListener_A01_t05.dart b/LibTest/html/IFrameElement/addEventListener_A01_t05.dart
index 4d8d9ab87c..ed1b945112 100644
--- a/LibTest/html/IFrameElement/addEventListener_A01_t05.dart
+++ b/LibTest/html/IFrameElement/addEventListener_A01_t05.dart
@@ -17,7 +17,7 @@ main() {
 
   var n = 10;
 
-  asyncMultiStart(n);
+  asyncStart(n);
 
   EventListener genHandler() => (e) {
         Expect.equals(type, e.type);
diff --git a/LibTest/html/IFrameElement/addEventListener_A01_t06.dart b/LibTest/html/IFrameElement/addEventListener_A01_t06.dart
index 33a5d20b96..78f14bf9e7 100644
--- a/LibTest/html/IFrameElement/addEventListener_A01_t06.dart
+++ b/LibTest/html/IFrameElement/addEventListener_A01_t06.dart
@@ -17,7 +17,7 @@ main() {
 
   var n = 10;
 
-  asyncMultiStart(n);
+  asyncStart(n);
 
   EventListener genHandler() => (e) {
         Expect.equals(type, e.type);
diff --git a/LibTest/html/IFrameElement/removeEventListener_A01_t01.dart b/LibTest/html/IFrameElement/removeEventListener_A01_t01.dart
index 6750dcf81b..db39b84274 100644
--- a/LibTest/html/IFrameElement/removeEventListener_A01_t01.dart
+++ b/LibTest/html/IFrameElement/removeEventListener_A01_t01.dart
@@ -33,7 +33,7 @@ main() {
   x.addEventListener(type, handler1);
   x.addEventListener(type, handler2);
 
-  asyncMultiStart(3); // first time two handlers, second time one handler
+  asyncStart(3); // first time two handlers, second time one handler
   var event = new Event(type);
   x.dispatchEvent(event);
   event = new Event(type);
diff --git a/LibTest/html/IFrameElement/removeEventListener_A01_t02.dart b/LibTest/html/IFrameElement/removeEventListener_A01_t02.dart
index 69c28d431f..2db18697b8 100644
--- a/LibTest/html/IFrameElement/removeEventListener_A01_t02.dart
+++ b/LibTest/html/IFrameElement/removeEventListener_A01_t02.dart
@@ -35,7 +35,7 @@ main() {
   body?.addEventListener(type, handler1, true);
   body?.addEventListener(type, handler2, true);
 
-  asyncMultiStart(3); // first time two handlers, second time one handler
+  asyncStart(3); // first time two handlers, second time one handler
   var event = new Event(type);
   x.dispatchEvent(event);
   event = new Event(type);
diff --git a/LibTest/html/Node/addEventListener_A01_t01.dart b/LibTest/html/Node/addEventListener_A01_t01.dart
index 986da05643..4028c7d6bb 100644
--- a/LibTest/html/Node/addEventListener_A01_t01.dart
+++ b/LibTest/html/Node/addEventListener_A01_t01.dart
@@ -31,7 +31,7 @@ main() {
     document,
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/addEventListener_A01_t02.dart b/LibTest/html/Node/addEventListener_A01_t02.dart
index 107f5a57b0..8fde6c8084 100644
--- a/LibTest/html/Node/addEventListener_A01_t02.dart
+++ b/LibTest/html/Node/addEventListener_A01_t02.dart
@@ -29,7 +29,7 @@ main() {
     document,
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/addEventListener_A01_t03.dart b/LibTest/html/Node/addEventListener_A01_t03.dart
index a07710e123..789014b6a4 100644
--- a/LibTest/html/Node/addEventListener_A01_t03.dart
+++ b/LibTest/html/Node/addEventListener_A01_t03.dart
@@ -31,7 +31,7 @@ main() {
     document,
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/addEventListener_A01_t04.dart b/LibTest/html/Node/addEventListener_A01_t04.dart
index 0eb6530534..7f18dcdafa 100644
--- a/LibTest/html/Node/addEventListener_A01_t04.dart
+++ b/LibTest/html/Node/addEventListener_A01_t04.dart
@@ -32,7 +32,7 @@ main() {
     document,
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/addEventListener_A01_t05.dart b/LibTest/html/Node/addEventListener_A01_t05.dart
index bac42c2357..447e33bfcf 100644
--- a/LibTest/html/Node/addEventListener_A01_t05.dart
+++ b/LibTest/html/Node/addEventListener_A01_t05.dart
@@ -34,7 +34,7 @@ main() {
     document,
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length * n);
+  asyncStart(targets.length * n);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/dispatchEvent_A01_t01.dart b/LibTest/html/Node/dispatchEvent_A01_t01.dart
index 2241b2da51..189fa85962 100644
--- a/LibTest/html/Node/dispatchEvent_A01_t01.dart
+++ b/LibTest/html/Node/dispatchEvent_A01_t01.dart
@@ -24,7 +24,7 @@ main() {
     new IFrameElement(),
     document,
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/on_A01_t01.dart b/LibTest/html/Node/on_A01_t01.dart
index af26e1abe3..e6704b2baf 100644
--- a/LibTest/html/Node/on_A01_t01.dart
+++ b/LibTest/html/Node/on_A01_t01.dart
@@ -25,7 +25,7 @@ main() {
     new IFrameElement(),
     new DocumentFragment(),
   ];
-  asyncMultiStart(targets.length);
+  asyncStart(targets.length);
   for (Node x in targets) {
     check(x);
   }
diff --git a/LibTest/html/Node/removeEventListener_A01_t01.dart b/LibTest/html/Node/removeEventListener_A01_t01.dart
index 36757aac2a..db1565b39d 100644
--- a/LibTest/html/Node/removeEventListener_A01_t01.dart
+++ b/LibTest/html/Node/removeEventListener_A01_t01.dart
@@ -43,7 +43,7 @@ main() {
     new Comment("Comment"),
     new DocumentFragment(),
   ];
-  asyncMultiStart(
+  asyncStart(
       targets.length * 3); // first time two handlers, second time one handler
   for (Node x in targets) {
     check(x);
diff --git a/LibTest/html/Node/removeEventListener_A01_t02.dart b/LibTest/html/Node/removeEventListener_A01_t02.dart
index 715eaa04a6..bacd9632dd 100644
--- a/LibTest/html/Node/removeEventListener_A01_t02.dart
+++ b/LibTest/html/Node/removeEventListener_A01_t02.dart
@@ -43,7 +43,7 @@ main() {
     new Comment("Comment"),
     new DocumentFragment(),
   ];
-  asyncMultiStart(
+  asyncStart(
       targets.length * 3); // first time two handlers, second time one handler
   for (Node x in targets) {
     check(x);
diff --git a/LibTest/io/File/create_A02_t01.dart b/LibTest/io/File/create_A02_t01.dart
index f828b56c23..6936fd46a7 100644
--- a/LibTest/io/File/create_A02_t01.dart
+++ b/LibTest/io/File/create_A02_t01.dart
@@ -49,7 +49,7 @@ _test(Directory sandbox, {bool exclusive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, exclusive: false);
   await _test(sandbox, exclusive: true);
 }
diff --git a/LibTest/io/File/create_A02_t02.dart b/LibTest/io/File/create_A02_t02.dart
index 7bdf0254e4..af2097053f 100644
--- a/LibTest/io/File/create_A02_t02.dart
+++ b/LibTest/io/File/create_A02_t02.dart
@@ -47,7 +47,7 @@ _test(Directory sandbox, {bool exclusive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, exclusive: false);
   await _test(sandbox, exclusive: true);
 }
diff --git a/LibTest/io/File/create_A03_t01.dart b/LibTest/io/File/create_A03_t01.dart
index 3a2b5002fc..4d9abf1428 100644
--- a/LibTest/io/File/create_A03_t01.dart
+++ b/LibTest/io/File/create_A03_t01.dart
@@ -48,7 +48,7 @@ _test(Directory sandbox, {bool recursive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, recursive: false);
   await _test(sandbox, recursive: true);
 }
diff --git a/LibTest/io/File/create_A03_t02.dart b/LibTest/io/File/create_A03_t02.dart
index a81c9a459c..8876361411 100644
--- a/LibTest/io/File/create_A03_t02.dart
+++ b/LibTest/io/File/create_A03_t02.dart
@@ -48,7 +48,7 @@ _test(Directory sandbox, {bool recursive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, recursive: true);
   await _test(sandbox, recursive: false);
 }
diff --git a/LibTest/io/File/create_A03_t03.dart b/LibTest/io/File/create_A03_t03.dart
index 6e7b895f62..724c2100a2 100644
--- a/LibTest/io/File/create_A03_t03.dart
+++ b/LibTest/io/File/create_A03_t03.dart
@@ -57,7 +57,7 @@ _test(Directory sandbox, {bool recursive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, recursive: false);
   await _test(sandbox, recursive: true);
 }
diff --git a/LibTest/io/File/create_A03_t04.dart b/LibTest/io/File/create_A03_t04.dart
index c20e14cfc5..70770ae305 100644
--- a/LibTest/io/File/create_A03_t04.dart
+++ b/LibTest/io/File/create_A03_t04.dart
@@ -57,7 +57,7 @@ _test(Directory sandbox, {bool recursive = false}) async {
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(2);
+  asyncStart(2);
   await _test(sandbox, recursive: false);
   await _test(sandbox, recursive: true);
 }
diff --git a/LibTest/io/File/create_A04_t01.dart b/LibTest/io/File/create_A04_t01.dart
index c245b60777..b1ca6bc112 100644
--- a/LibTest/io/File/create_A04_t01.dart
+++ b/LibTest/io/File/create_A04_t01.dart
@@ -51,7 +51,7 @@ _test(Directory sandbox,
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(4);
+  asyncStart(4);
   await _test(sandbox, recursive: false, exclusive: false);
   await _test(sandbox, recursive: false, exclusive: true);
   await _test(sandbox, recursive: true, exclusive: false);
diff --git a/LibTest/io/File/create_A04_t02.dart b/LibTest/io/File/create_A04_t02.dart
index 17dfb09be1..485de8ea3f 100644
--- a/LibTest/io/File/create_A04_t02.dart
+++ b/LibTest/io/File/create_A04_t02.dart
@@ -52,7 +52,7 @@ _test(Directory sandbox,
 }
 
 void _main(Directory sandbox) async {
-  asyncMultiStart(4);
+  asyncStart(4);
   await _test(sandbox, recursive: false, exclusive: false);
   await _test(sandbox, recursive: false, exclusive: true);
   await _test(sandbox, recursive: true, exclusive: false);
diff --git a/LibTest/io/file_utils.dart b/LibTest/io/file_utils.dart
index 1e5c27e2f0..84cb1ddf3b 100644
--- a/LibTest/io/file_utils.dart
+++ b/LibTest/io/file_utils.dart
@@ -20,9 +20,11 @@ Future<Object?> inSandbox(Object? test(Directory sandbox),
     sandbox = getTempDirectorySync();
   }
   try {
+    asyncStart();
     return await test(sandbox);
   } finally {
     sandbox.deleteSync(recursive: true);
+    asyncEnd();
   }
 }
 
@@ -52,6 +54,7 @@ Future<void> testFileSystemEvent<T extends FileSystemEvent>(Directory root,
     if (failIfNoEvent) {
       Expect.fail("No event was fired for $eventsTimeout seconds");
     }
+    return null;
   });
   test(event);
 }
diff --git a/Utils/async_utils.dart b/Utils/async_utils.dart
index ad2c35e310..1c011d356b 100644
--- a/Utils/async_utils.dart
+++ b/Utils/async_utils.dart
@@ -31,34 +31,49 @@ Future runAfter(Future f, void action()) {
   });
 }
 
-/// Let the test driver know the test is asynchronous and continues after the
-/// method main() exits.
-/// See http://code.google.com/p/co19/issues/detail?id=423
+bool _initialized = false;
+int _asyncLevel = 0;
 
-Completer _completer = new Completer();
-Future asyncCompleted = _completer.future;
-
-int _asyncTestStart() {
-  print("unittest-suite-wait-for-done");
-  return 0;
-}
-
-int _asyncCounter=_asyncTestStart();
-
-void  asyncStart() {
-  _asyncCounter++;
+Exception _buildException(String msg) {
+  return Exception('Fatal: $msg. This is most likely a bug in your test.');
 }
 
-void  asyncMultiStart(int delta) {
-  _asyncCounter += delta;
+/// Call this method before an asynchronous test is created.
+///
+/// If [count] is provided, expect [count] [asyncEnd] calls instead of just one.
+void asyncStart([int count = 1]) {
+  if (count <= 0) {
+    return;
+  }
+  if (_initialized && _asyncLevel == 0) {
+    throw _buildException('asyncStart() was called even though we are done '
+        'with testing.');
+  }
+  if (!_initialized) {
+    print('unittest-suite-wait-for-done');
+    _initialized = true;
+  }
+  _asyncLevel += count;
 }
 
-void  asyncEnd() {
-  Expect.isFalse(_asyncCounter == 0, "asyncEnd: _asyncCounter==0");
-  _asyncCounter--;
-  if (_asyncCounter == 0) {
-    print("unittest-suite-success");
-    _completer.complete(null);
+/// Call this after an asynchronous test has ended successfully.
+///
+/// Note, that when all async tests are finished and `unittest-suite-success` is
+/// printed browser tests are successfully finished. So, there should be no any
+/// assertions after `asyncEnd()`. Otherwise the test may produce false-positive
+/// result
+void asyncEnd() {
+  if (_asyncLevel <= 0) {
+    if (!_initialized) {
+      throw _buildException('asyncEnd() was called before asyncStart().');
+    } else {
+      throw _buildException('asyncEnd() was called more often than '
+          'asyncStart().');
+    }
+  }
+  _asyncLevel--;
+  if (_asyncLevel == 0) {
+    print('unittest-suite-success');
   }
 }